Compression Pressure; Checking / Adjusting; Valve Clearance - Stihl 4180 Series Manual

7.1

Compression Pressure

– Pull the boot off the spark plug.
– Unscrew the spark plug.
: Screw compression tester
5910 850 2000 (1) into the spark
plug hole.
– Move slide control to "STOP-0".
– Set choke shutter to open.
– Pull starter rope vigorously and
quickly several times.
– Note compression pressure.
If the compression pressure is
below 6 bar, check valve clearance
and readjust if necessary, b 7.2.
If this produces no improvement,
check the cylinder, valve seat,
piston and piston rings for scores or
other damage.
The design specification is 6...7 bar.
Reassemble in the reverse
sequence.
32
7.2

Checking / Adjusting

Valve Clearance

Check and adjust valve clearances
only when engine is cold.
– Remove the rewind starter,
b 5.2
1
– Remove the shroud, b 5.7
: Take out the screw (1).
– Remove the sealing ring.
– Unscrew the spark plug.
: Remove the valve cover (1).
: Remove the gasket (2).
: Rotate the crankshaft until the
arrow (1) is in line with the screw
(2) on the right-hand side of the
ignition module.
Observe rocker arms while rotating
the flywheel up to the mark. If the
valves are operated by the rocker
arms in this position (valve overlap),
rotate the crankshaft another turn
until the valves are idle and the
arrow (1) lines up with the screw (2).
Turn the crankshaft back and forth
to make sure the valves are not
1
operated in this position.
If there is no noticeable valve
overlap, proceed as follows:
1
2
Series 4180 Powerhead
2
1